Biologics are commonly employed to promote bone growth in medical applications including fracture healing and surgical management of spinal disorders (1-4). Spine fusion is often performed by orthopedic surgeons and neurosurgeons alike to address degenerative disc disease and arthritis affecting the lumbar and cervical spine. Historically, autogenous bone graft, commonly taken from the iliac crest of the patient, has been used to augment fusion between vertebral levels. However, the associated donor site morbidity, increased operating time, and increased blood loss associated with harvesting autogenous bone graft (5-7) has provided incentive to find a safe and effective alternative.
Recombinant human bone morphogenetic protein-2 (rhBMP-2) is commonly used to promote spine fusion in humans. Its use was approved in 2002 by the US Food and Drug Administration (FDA) for single-level anterior lumbar interbody fusion (8). The use of rhBMP-2 has increased significantly since this time and indications for its use have expanded to include posterior lumbar spinal fusion as well cervical spine fusion. Despite the efficacy of rhBMP-2, recent reports have called into question its safety when employed during spine fusion surgery. Reported complications have included seroma formation, soft tissue swelling, vertebral osteolysis, ectopic bone formation, retrograde ejaculation, and carcinogenicity (9-12). Moreover, airway edema has been observed with its use in the cervical spine, prompting the FDA to issue a Public Health Notification warning for its use in cervical spine operations. To date no suitable alternative has been identified that would have similar efficacy in inducing fusion without the adverse effects of rhBMP-2 (12).
Oxysterols form a large family of oxygenated derivatives of cholesterol that are present in the circulation, and in human and animal tissues. Oxysterols have been found to be present in atherosclerotic lesions and play a role in various physiologic processes, such as cellular differentiation, inflammation, apoptosis, and steroid production. Some of the present inventors previously reported that specific naturally occurring oxysterols have robust osteogenic properties (13). The most potent osteogenic naturally occurring oxysterol, 20(S)-hydroxycholesterol (“20S”) (14), is both osteogenic and anti-adipogenic when applied to multipotent mesenchymal cells capable of differentiating into osteoblasts and adipocytes. Structural modifications of 20S were previously performed to synthesize more potent analogues of 20S including Oxy34 and Oxy49, which were shown to induce the osteogenic and inhibit the adipogenic differentiation of bone marrow stromal cells (MSC) through activation of Hedgehog (Hh) signaling (15). Additionally, Oxy34 and Oxy49 stimulate spine fusion in vivo in a rat model of posterolateral spine fusion (15). Prior oxysterol molecules have properties that vary widely and unpredictably. There remains a need for new improved oxysterols as compared with rhBMP-2 and prior oxysterols, to provide increased potency and enhanced efficacy, and ease of synthesis and lower production cost. A new oxysterol could make a more feasible clinical option for physicians treating, for example, long bone fractures, spine disorders, and osteoporosis.